unfortunately this is a common issue with iPhone8,8+ and iPhone X
Check out the other threads
Just send it back to sandisk for RMA
If your country is not supported, you can do manual RMA by emailing them
they are very efficient
better than the local distributor (for my case, Malaysia) who refused to send the defective (not working with iphone X) ixpand to the HQ for RMA and offered store credits instead.
